Astronomers have detected an 'impossible Dust Ring' at the heart of our solar system

In this illustration, several dust rings circle the Sun. These rings form when planets’ gravities tug dust grains into orbit around the Sun. Recently, scientists have detected a dust ring at Mercury’s orbit. Others hypothesize the source of Venus’ dust ring is a group of never-before-detected co-orbital asteroids. Credits: NASA’s Goddard Space Flight Center/Mary Pat H

Our solar system is filled with dust from crumbling asteroids and comets, but only a few planets have a grainy ring of their own. Both Venus and earth have them, escorted around the sun by a band of cosmic matter. 

The smallest and nearest planet to sun Mercury, was once thought to be all alone. Pressed right up against the solar system's only energy source, scientists could never have imagined that dust could survive here. But it turns out we were wrong. 

A new study has now identified a vast trail of fine cosmic dust in Mercury's orbit, forming a ring nearly 15 million km wide (9.3 million miles). 

It is likely that Mercury has been wading through this sea of ancient matter for billions of years which is three times bigger than itself. 

"People thought that Mercury, unlike Venus and Earth, is too small and too close to sun to capture a dust ring", says co-author Guillermo Stenborg, a solar scientist at the Naval Research Laboratory. 

"They expected that solar wind and magnetic forces from sun would blow any excess dust at Mercury's orbit away", he added. 

In truth, Stenborg and Russell Howard, a fellow scientist, stumbled up their discovery by accident. The team was actually looking for gaps in the dust, close to the sun where matter should have been vaporised and swept clean. 

With all the dust obscuring our immediate vision, scientists haven't been able to find any dust free spaces between us and sun. From where we are sitting, it simply looks like there's dust everywhere. 

The only clues we have are the different types of light we see shining back to us. When sunlight bounces off of the dust particles in space, it creates a force 100 times brighter than coronal light itself. 

Most of the time, scientists throw this data away so they can focus solely on studying the corona, but this time, on a whim, researchers kept it. 

Using pictures of interplanetary space from NASA's STEREO satellite, the team built a model that separates both kinds of light, calculating how much dust is really out there.

This visualization displays a simulation of the dust ring at Venus’ orbit around the Sun. Scientists hypothesize a group of never-before-detected asteroids orbiting the Sun with Venus are responsible for supplying Venus’ dust ring. Credits: NASA’s Scientific Visualization Studio/Tom Bridgman

What they noticed was an enhanced brightness circling all the way around Mercury's orbit, implying "an excess dust density of about 3 to 5 percent at the center of the ring". 

"It wasn't an isolated thing", says Howard. "All around the sun, regardless of the Spacecraft's position, we could see the same five percent increase in dust brightness and density. That being said, something was there, and it's something that extends all around the sun". 

The results have pushed our understanding right to the brink. Because if Mercury really does wade through cosmic dust, then this material must be able to get far closer to the sun than we ever thought to be possible. 

This in turn, gives scientists important clues about the composition and origin of the dust itself. 

Researching dust rings in our solar system is not at all that different to reading tree rings in the forest. Composed of ancient rubble from 4.6 billion years ago, orbiting clouds of dust could help us explain what has happened since our solar system first formed. 

In fact, scientists think that all the planets in our solar system, including earth, started off as mere grains of dust before they were pulled together by gravity and other forces. 

Scientists think planets start off as mere grains of dust. They emerge from giant disks of gas and dust that circle young stars. Gravity and other forces cause material within the disk to collide and coalesce. (illustration). Credits: NASA’s Jet Propulsion

"In order to model and accurately read the dust rings around other stars, we first have to understand the physics of dust in our own Backyard", says Kuchner.

The massive dust ring that co-orbits Venus is a good start. Just this month, a new paper claims to have figured out the true source of Venus's massive dust ring, which is made up of grains no bigger than coarse sandpaper. 

Using dozens of different modelling tools and simulations, the researchers think the dust comes from a group of previously unseen asteroids co-orbiting with the planet.

Moreover, the authors argue that this population of crumbling asteroids has been feeding Venus's dust ring ever since the birth of solar system.

"It's not everyday you get to discover something new in the inner solar system", says Mark Kuchner, an astrophysicist at NASA's Goddard Space Flight Center and author on the Venus study. "This is right in our neighbourhood", he further adds.

The study has been published in the Astrophysical Journal Letters.